In known and conventional automatic and semi-automatic weapons, the back pressure of propellant gas and/or recoil is utilized to effect a complete firing cycle, i.e., extracting a spent cartridge form the firing chamber, ejecting the spent cartridge from the breech, cocking, loading and chambering a fresh cartridge and locking the bolt. When blank, or practice, ammunition is utilized, as would be the case with training operations which are intended to simulate combat conditions or with theatrical, cinematic or other kinds of staged productions where realistic weapon-firing scenes are involved, the relatively low propellant gas pressure and recoil forces are incapable of operating the firearm in the automatic or semi-automatic mode.
In order to overcome this problem, a variety of blank firing attachments or recoil boosters have been provided, the purpose of which is to increase the back pressure of the propellant gas and/or recoil to the point where such pressure and/or recoil force will be sufficient to operate the weapon in the automatic or semi-automatic mode.
An example of a blank firing attachment is described in U.S. Pat. No. 2,075,837, and includes a plug having a central longitudinal bore and flared conical mouth which is screwed into a barrel jacket that has been fitted over the muzzle of the barrel. The plug increases the back pressure of the firearm, a Browning machine gun, to permit the weapon to be automatically operated.
Another example of a blank firing attachment is disclosed in U.S. Pat. No. 3,744,370. A blank firing attachment is installed on a slotted flash suppressor-equipped firearm, the firearm including an externally mounted open frame member fitted at one end to an annular recess defined within a first suppressor. A rod like restrictor is engaged in axial alignment with the bore of the barrel.
A third example of a blank firing attachment is U.S. Pat. No. 2,714,332. This device possesses a recoil amplifier fitted to the barrel of a machine gun. The recoil amplifier includes a gas chamber situated in front of the muzzle at the barrel and closed by a perforated disk.
A fourth example is French Pat. No. 529,545 and includes a plug with a gas-occluding passage therethrough. The plug is held in place against the crown of a gun barrel by a threadedably engagable element. The gas-occluding passage, which terminates in a conical zone defined upon the rear face of the plug, possesses a length which, in the embodiments shown, exceeds the diameter of the plug.
Other blank firing devices similar in operational principle, if not in design, to the preceding arrangements
are described in U.S Pat. Nos. 2,330,210, 2,805,602, 3,137,204, 3,363,509, 3,369,453, 3,411,229, 3,440,924, 3,687,000, 3,732,775, 3,941,029 and 4,499,811.
The aforementioned devices are subject to one or more disadvantages which limit their usefulness. For example, they are relatively structurally complex, involve modification of the firearm and/or are not easily or quickly installed. Most of the known devices, i.e., the previously described U.S. Pat. Nos. 3,744,370 and 2,714,332 result in an obvious alteration in the outward appearance of the firearms in which they are installed. While this may not be considered a significant problem for military applications, a firearm having an altered outward appearance is highly disadvantageous where staged entertainments are concerned. In the latter type of situation, any deviation from reality could detract from the verisimilitude of a scene thus impairing its entertainment value.
Another shortcoming of prior art devices is their difficulty in functioning in an effective manner consistent with normal operation of a semi-automatic or automatic weapon, particularly an M-16 rifle. As will be described later in further detail, a series of tests were performed on certain known devices and the present invention to determine the overall effectiveness and operability of each unit. Results of these tests demonstrated that in operation with an M-16 rifle, the present invention is superior over known devices of like construction which experienced severe operating difficulties and excessive temperature and pressure buildups in their units.